Selexys Pharmaceuticals is developing a humanized monoclonal antibody drug called SelG1 directed against P-selectin for the treatment of vasoocclusive crisis in patients with sickle cell disease. The ultimate goal of this Phase IIB proposal is to further advance SelG1 into Phase II/III safety and efficacy trials to support of regulatory filings for FDA approval and commercialization. Previous work funded in part by an NHLBI SBIR Fast Track award R44HL093893, and Selexys financing, resulted in the completion of studies to determine the pharmacology/toxicology of SelG1 in cynomolgus monkey, filing the SelG1 IND with the FDA and the completion of a Phase I safety and PK/PD normal volunteer study. The final audited Phase I study report will be submitted to the IND in Q1 2012. The aims of this proposal are directed to the conduct and analysis of a Phase II clinical efficacy and safet study to evaluate SelG1 as a therapeutic treatment for sickle cell patients. Sickle cell disease (SCD) affects over 90,000 individuals in the US and remains a debilitating condition with major unmet medical need leading to high morbidity and mortality. Selexys is developing SelG1 as a once monthly IV infusion for the prevention or reduction of vasoocclusive crisis and associated morbidities in sickle cell patients. The company has engaged in planning with key opinion leaders (KOLs) in the SCD field to develop a clinical protocol for SelG1 to be conducted in a Phase II safety and efficacy trial in approximately 120 SCD patients, powered to >88% for the validated primary endpoint of sickle cell crisis reduction. The planned study would be a 12- month double-blinded, randomized, placebo-controlled 3-arm study with two SelG1 dosing arms. The manufacturing plan is set to commence in Q1 2012 with GMP production of SelG1 at the 500-1000L scale at Cytovance Biologics in Oklahoma City. Patient recruitment and conduct of the study is projected to commence in Q2-Q3 of 2012 with an overall study duration of 18-24 months. The funds requested in this PhIIB renewal application are for support of conduct and management of the clinical program, bioanalytical assays, and analysis of the clinical trial results. It is anticipated that successful completion of the Phase II study will lead to a pivotal Phase III safety and efficacy trial with the goal of registration, FDA approval and launch of SelG1 for the treatment of vasoocclusive crisis in sickle cell patients.